Loud speaker



C. MIDHAT Nov.' 3, 1931.

LOUD SPEAKER Filed April 7, 195o -sheets-sheet 1 Nov. 3, 1931. c. MIDHAT 1,829,910

LOUD SPEAKER Filed April '7, 1930 4 Sheets-Sheet. 2

Nov, 3, 1931'. C, MIDHAT 1,829,910

LOUD SPEAKER Filed April '7. 1930 4 Sheets-Sheet 3 fig. 4

Nov. 3, 1931.

c, MIDHAT LOUD SPEAKER Filed April 7, 1930 4 Sheets-Sheet 4 Patented Nov. 3, 1931 PATENT OFFICE CHAKIR MIDHAT, OF BERLIN-EICHKAMP, GERMANY LOUD SPEAKER Application led April 7, 1930, Serial No. 442,430, and in Germany April 18, 1929. y

This invention relates to loudspeakers of the type in which the driving unit is used for causing oscillations not only of the diaphragm, but of a plurality of strings, too. Tn

a constructional form of loudspeakers of this type which is described and shown in my 'copending United 'States patent application Serial Number' 321,256, iled November 22, 1928, the diaphragm is located in front of the sounding boX. This arrangement entails a drawback in that, if the diaphragm, for the purpose of attaining a better reproduction of the lower tones, is provided with a baffle board, the largest part of the soundl5 ing boX with the strings thereon is covered vso that the vibrations of the strings cannot radiate or propagate forwardly to their enltire eXtent. This drawback is obviated in my present improved constructional form of 20 a loudspeaker of the type in question by a more suitable configuration of the sounding boX.

In the above-mentioned known constructional form of a stringed loudspeaker the l' 25 strings are firmly coupled with the driving .unit by means of a connecting member so that the oscillations of the driving unit are transmitted to the strings without any diminution. This method of employing a firm coupling is, generally speaking, well useful,but entails, nevertheless, the drawback that if the driving unit is very powerful, the strings are oscillated very strongly,

whereby the reproduction by the loudspeaker, as regards certain performances, is felt as being too rich in higher harmonics and, therefore, not quite in correspondence with the original performance. For this reason the known constructional form of the loudspeaker has, by my present invention, been modified in such a manner that there is no firm connection between the strings and the driving unit. The oscillations are transmitted to the string system only in this way that this system leans with a slight pressure against the movable part of the driving unit so that an elastic contact arises. It is now possible to render the transmission of the oscillations to the strings variable, in cono* forniity with the character of the reproduced is a front-view of a modiiication in which c two sounding boxes are provided; Figure 4 is a perspective representation of the loudspeaker in which the strings form two sets, the lower part of the ligure being broken away; Figure 5 is a vertical section through parts of the strings of said two sets, a part of the diaphragm, and the connecting and transmitting members; Figure 6 is a sideview of certain of these members, and ligure 7 is a plan of them, all as fully described hereinafter.

Referring to Figs. 1 and 2, S denotes the driving unit, by which the diaphragm d, as well as the strings a, are caused to oscillate. is the sounding box to which the diaphragm d is attached by means of a ring j' consisting of soft leather or another suitable soft material.

The sounding box surrounds the diaphragm Z on all sides like a balie board so that the oscillations of the diaphragm, as well as those of the sound box, can directly radiate towards both sides without disturbing one another.

Such a construction of the sound boX presents, further, the great advantage that it considerably assists theinost'uniform possible reproduction of the whole acoustic scale by the loudspeaker and for the reason which will be hereinafter explained. -Vy/hen a large-.

Vsurface diaphragm produces the. lower tones, `the slow air-oscillations corresponding to these tone ranges on either side of the diaphragm have, as is known, the tendency to equalize around the rim of the diaphragm.

Tn order to obivate this, a sound baffling board is usually arranged around the rim of the diaphragm. As in the loudspeaker according to this invention instead of the rigid baffle board a sounding box is used, its effect is, so to say, a double one. It not only prevents the direct equalization of the air vibrations corresponding to the lower tone ranges, but intensifies them at the same time by resonance. The air vibrations, however, corresponding to the higher tone ranges which propagate, as is generally known, straight forward in the direction of the diaphragm axis are subjected, according to the frequency, to the strengt-hening effect either only little or not at all. By this resonance strengthening of mainly only lower tone ranges neglected by the diaphragm a very uniform reproduction of the whole acoustic scale is obtained.

Approximately a similar effect is attained if, instead of one large sounding board suirounding the diaphragm on all sides, a plurality ofsmaller boards or sounding boxes arranged around the diaphragm is used. In this case the sounding boxes can also be such as used in connection with ordinary stringed instruments, such as bow instruments, zithers, and other plucking instruments. Such a construction, although being somewhat complicated, maybe very well useful for certain purposes, as with it the species of the respective instruments are rendered discernible with absolute certainty, and by making use of more valuable instruments the tone-color or timbre of the loudspeaker can be considei'- ably improved, beautified, and ennobled.

Figure 3 shows a constiuctional form having two sound boxes, oneabove and the other be ow the diaphragm, Fig. 2 showing also the longitudinal section of this form of construction. vThe const-ructional form shown in Fig. 3 presents, in comparison to that of Fig. 1, the advantage on the one hand that eX- pensive sounding wood is saved, and on the other hand that inthis manner the loud speaker can be considerably smaller. The louds eaker shown in Fig. 3 has preferably two lids e which when open serve as lateral vsound bathing plates and when closedas protective lids. 4

As has already been mentioned in a preceding part of this specification, the strings are not firmly connected with the driving unit, and the oscillations are transmitted to the strings solely by elastic contact. This method of transmitting the oscillations presupposes that the string system, viewed as a whole,

has in itself a sufiicient elastic force, that is to say, that it is able to oppose the reciprocating movements ofthe driving unit with an elastic force. This presupposition cannot, in the known constructional form mentioned in the introductory part of this speciication, be responded to in a quite satisfactory manner, as with that method all strings lie in one plane so that the elastic force of the entire string system is comparatively weak. This resilient force might be strengthened by using short strings put under strong tension,

this presenting, however, again the inconvenience that the individua-l vibrations of the individual strings become then only feeble so that they cannot give ott a great volume of sound. l

In the perspective view Fig. 4 a modification of the known tensioning method of the strings is illustrated which permits to increase considerably the resilient effect of the whole string system without the necessity to stretch too strongly the individual strings. As shown, some of the strings are connected with the disc c1, the remaining strings being connected with a similar disc c2. T he discs are spaced from one another by an intermediate member lc. It is evident that at a similar tension of the individual strings the resilient force of the whole string system becomes the i'eater, the more the two discs are remote Trom one another. In this manner the elastic force of the whole string system can be accommodated to the purpose by suitably selecting the length of the intermediate member k and the tensions of the individual strings. For the operation of the loudspeaker it is immaterial whether the two discs c1 and 02 and the intermediate member k are separate pieces or are made in one piece.

This string tensioning method is very well suited for use in connection with the method of transmitting the oscillations as employed in tlie present improved loudspeaker With the aid of an elastic Contact. The constructional form shown in Figs. 5, 6 and 7 is designed in this way. The strings a are connected with the two disks vc1 and c2 in the manner described with respect to Fig. 4, and said disks are kept suitably apart' from one another by means of a rod c provided at one end with a knob o and at the other end with a sector l (Figs, 5-7) consisting of metal or another suitable hard material and bearing a layer m of a material, the hardness of which decreases from one endy of the sector to the other end, as is indicated in Fig. 5 by different dotting of said layer m in vertical direction. This layer may consist of felt, leather, rubber, or the like, or of a combination of these or other, more or less elastic substances.

The sector Z/m, more precisely the layer m, can be adjusted by means of the knob o which can be turned in the one or in the other direction, which is eil'ected always in this way that the layer m presses slightly onto the tip p1 of the driving pin p with which the diaphragm d is firmly coupled. According to the character of the reproduced music the sector l/m may be so adjusted that either a harder or a softer portion of the layer m contacts with the tip p1 whereby the strings are caused to oscillate stronger or lesser, as required.

If the sector l/m isvso adjusted that the layer m does not contact with the tip p1 in which case the position of the sector is that indicated by 'dotted lines in Fig. 5, no oscillations are transmitted to the strings so that if, for instance, speech is to be reproduced, solely the diaphragm is actuated.

I claim:

1. A loudspeaker, comprising, 1n combination, a large-sized diaphragm, a resonance box surrounding said diaphragm on all sides likev a baffle-board, a plurality of strings stretched over said resonance box, and a driving unit adapted to cause said diaphragm, as Well as said strings, to oscillate, substantially as set forth.

2. A loudspeaker, comprising, in combination, a large-sized diaphragm, a plurality of resonance bodies arranged around said diaphragm, a plurality of strings stretched over said resonance bodies, and a driving unit adapted to cause said diaphragm, as Well as said strings, to oscillate, substantially as set 3. A loudspeaker, comprising, in combination, a large-sized diaphragm, a resonance box, a plurality of strings attached at one end to said resonance box, a disk connected With the other ends of some of said strings, a similar disk connected with the other ends of the remaining strings, an intermediate member spacing said disks, a driving unit coupled with said diaphragm, and means for transmitting the oscillations from said driving unit t'o said strings in a variable degree, substantially as set forth.

4. A loudspeaker, comprising, in combination, a large-sized diaphragm, a resonance box, a plurality of strings attached at one end to said resonance box, two like disks connected with the other ends of the strings, a rod spacing said disks, a sector attached firmly to the one end of said rod, a damping 40 layer of varying hardness attached to said sector, and a driving unit coupled With said diaphragm, said sector being adapted to make a spring Contact With the moving part of the driving unit, substantially as set forth.

In testimony whereof I affix my signature.

` CHAKIR MIDI-IAT. 

